The whole-body content of androgen (testosterone + 5 alpha-dihydrotestosterone) was significantly higher on Fetal Days 18 and 19 in male than in female rats; androgen content was equivalent in the two sexes at other fetal ages, including Days 16, 17, 20, and 21, and prior to parturition on Fetal Day 22. These results partially corroborate previous data of Weisz and Ward (Endocrinology 1980; 106:306-316), who measured testosterone in pooled plasma from rat fetuses and suggest that androgens contribute to masculine brain sexual differentiation only briefly during fetal life. No significant differences in whole-body androgen content were observed among groups of females situated in utero between 0, 1, or 2 males on each side (contiguous male model) or among groups of females with 0, 1, or 2 or more males located caudally (on the cervical side) in the same uterine horn, regardless of whether combined data from Fetal Days 17-22 or only Fetal Days 18 and 19 were considered. These results provide no evidence that androgens from males reach female fetuses in the same uterine horn.

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Testosterone propionate (TP) was given to rats on days 16 through 20 of pregnancy (2 mg/day). Female young had masculinized external genitalia. Sexual maturity was accelerated in TP females, despite lower weights and shorter lengths of body and tail. Placental and body weights were lower in TP females and males than in controls. The inhibiting effect of TP on postnatal growth is probably mediated by its effect on birth weight through placental damage. Ovarian cyclicity occurred upon reaching sexual maturity. In one experiment TP females were ovariectomized at 6 weeks, and given ovarian and vaginal grafts. Most of these animals showed regular cyclicity in vaginal smears between 74\p=m-\100 days. Thus neither the 'early', nor the 'delayed early androgen syndrome' occurred in these experiments.This absence of effect of prenatal TP on ovarian cyclicity is attributable to a placental barrier for testosterone. When maternal plasma testosterone was raised 20-fold by exogenous TP, foetal testosterone levels remained unchanged. More detailed information was obtained when labelled testosterone was infused into a pregnant rat.

Testosterone was measured in plasma pools from male and female fetal guinea-pigs between the ages of 30 and 55 days of pregnancy. Between days 33 and 36 the testosterone concentration in the plasma of males (1.4 ng/ml) was several times higher than that found at other ages or that measured in female fetuses. After infusion of tritiated testosterone for 2 h into pregnant guinea-pigs at day 36 of pregnancy, high levels of testosterone and androstenedione were found in maternal plasma. Nevertheless, tritiated testosterone and androstenedione could hardly be shown in the fetuses. Similar large differences in plasma progesterone levels appeared to exist between the maternal and the fetal circulation. Therefore, only a very small fraction of these steroids can penetrate from the maternal circulation into that of the fetus. This finding might be explained by the large difference in androgen-binding capacity between maternal and fetal plasma, as was shown by equilibrium dialysis.

To determine changes in steroidogenesis by rat ovaries during sexual maturation, ovaries obtained at various ages (days 10-35) and at the first pro-oestrus were incubated in the absence or presence of LH and the accumulation of steroids in the medium was measured. Basal and LH-stimulated oestradiol-17 beta and testosterone release into the medium, expressed in pmol/4 h per mg ovary, was high at day 10 of age and at first pro-oestrus. Between days 20 and 35 basal oestradiol and testosterone release was low and could not be stimulated by LH. Addition of testosterone to the culture medium increased oestradiol production at all ages studied. Release of progesterone occurred at all ages even in LH-free medium. Incubation in the presence of LH resulted in a dose-dependent increase in progesterone with a maximal response at pro-oestrus. Androsterone and 5 alpha-androstane-3 alpha,17 beta-diol production in the absence or presence of LH was high during the entire prepuberal period. Production of 5 alpha-reduced androgens in response to LH increased from days 10 to 20 but decreased thereafter. Similarly, 5 alpha-reductase activity, measured in ovarian homogenates, increased from days 10 to 20 but was decreased again by first pro-oestrus. A further decrease in basal and LH-stimulated 5 alpha-reduced androgen production occurred after first ovulation. These results demonstrated age-related changes in steroid release after in-vitro incubation. At day 10 progesterone can be converted to aromatizable androgens allowing production of oestrogens, while after day 10 progesterone is converted to 5 alpha-reduced C19 steroids.(ABSTRACT TRUNCATED AT 250 WORDS)